Cholesterol contributes significantly to the mass of advanced atherosclerotic lesions. While biochemical analysis has established that both non-esterified and esterified cholesterol occur within lesions, analysis of whole lesions gives no indication of the relationship of these two forms of cholesterol to one another or to other lesion elements. Using different histochemical probes for non-esterified and esterified cholesterol, this project has established that these two cholesterol forms occupy discrete foci within lesions. This discrete localization of non-esterified and esterified cholesterol must be taken into account in any consideration of the mechanism of cholesterol deposition, or cholesterol efflux from atherosclerotic lesions.